If you post often, you will see an immediate spike in News Feed impressions, but it’s generally not worth the cost in lost fans. When your fans see two status updates from you in their News Feeds, they’ll likely get annoyed, and will consequently unsubscribe or un-fan. There are few exceptions to this rule.

If you post too infrequently, you’re missing out on opportunities to reach your fans. Over the course of a year, a page with 10,000 fans that posts only half as often as they could misses more than 1 million chances to get their content in front of a hyper-targeted Facebook audience. The larger your fan page, the more often you should be posting — without annoying your fans.

The kicker: Each post performs differently. Some posts last ten hours, and some posts last thirty hours.

Calculate the average post lifetime by using the method below, but remember it’s just that — an average. To get really in-depth, figure the average post lifetime for photos vs. articles, or the average lifetime when you post Thursdays at 3 p.m. vs. Saturdays at 10 a.m. However, it’s still just an average; each post is unique, so you can never exactly predict how it will perform.

How do you know when a post stops appearing in your fans’ News Feeds?

The good news is that when you track your posts’ performance, you’ll be able to see, in real-time, when that post drops out of the News Feed. If it flops five hours sooner than you expected, then immediately stick up a new post.

Each status update drops out of different fans’ News Feeds at different times, depending on how long Facebook’s algorithm EdgeRank calculates that particular fan will be interested in that particular status update. Then, the best we can do is look at how each status update performs across all your fans’ News Feeds.

You’ll actually see a slowdown in new impressions, clicks, likes and comments as a post starts dropping out of News Feeds. The following graphs show cumulative numbers, so when the graph flattens, the post has dropped out of News Feeds.

Each of these metrics has pros and cons.

1. Impressions per-post: Impressions per-post is a single aggregate count of how many times a particular status update has been viewed. Facebook updates this number as more and more people view the post; however, it often won’t update for several hours at a time when Facebook’s computers are calculating for millions of posts across millions of fan pages. On the bright side, when it works, it’s great — you can literally watch as your post gets viewed by fans.

2. Comments per-post: All the comments on any status update are time-stamped, so you can measure on a minute-by-minute basis exactly when a fan saw the status update. Unfortunately, most status updates receive so few comments that there aren’t enough data points to determine whether your fans are choosing not to comment or simply aren’t seeing the post in their News Feeds.

3. Likes per-post: In general, this is the most accurate way to see when your status update starts dropping out of News Feeds. Facebook updates the post’s like count in near real time, so it’s more reliable than the post impression count. And because posts tend to get more likes than comments, the data presents an accurate picture of how long a post stayed in News Feeds. On the other hand, likes aren’t time-stamped, so you have to check the like count regularly to see when new likes are added.

So how do I actually measure?

Post a status update. Every hour, record the number of impressions, likes and comments. Figure out when the rate of new impressions or likes slows down.

Try recording all the raw data in Excel, then graph the data just like you see above. Visually estimate the post lifetime based on when the graph flattens out.

After you calculate the post lifetime for 10-20 posts, you’ll start to generate an average post lifetime unique to your fan page.

What’s the average post lifetime?

I don’t know.

However, I surveyed 20 posts across five fan pages that had 2 million+ fans, and calculated an average post lifetime of 22 hours, 51 minutes. Theoretically, this implies most fan pages shouldn’t post more than once a day.

I strongly recommend keeping track of your posts in real-time because post lifetimes vary widely, even across the same fan page. In my sample of twenty posts, the shortest post lasted only 10 hours, while the longest post lasted a full 50 hours!

If you weren’t tracking those posts, you would have been invisible in the News Feed for 13 hours when the post flopped at the 10-hour mark. Similarly, you could have delayed your next post when the high-performing post showed no sign of slowing down.

Lastly, feel free to experiment and break the rules.

You won’t know if your fans respond better to a different posting strategy until you try it. Use these analytics to augment your intelligence, not replace it.